Diesel oil improvers



United States Patent DIESEL OIL IMPROVERS Charles L. Levesque, Philadelphia, Pa., assignor to Rohm & Haas Company, Philadelphia, Pa., a corporation of Delaware No Drawing. Application November 9, 1955 Serial No. 545,996

Claims. (Cl. 4457) This invention relates to improved diesel fuel oils and more specifically it deals with improved diesel fuel oil compositions of high cetane numbers. These compositions comprise a diesel fuel oil and have dissolved therein an amount of an azo compound as herein defined sufficient to improve the cetane rating thereof.

The performance of diesel fuel oil for compressionignition engines is closely related to the length of time of ignition of the fuel. The ignition delay of a diesel fuel oil'from the beginning of the injection of the fuel to the beginning of its combustion is commonly termed the ignition delay characteristic of the fuel. This characteristic may be expressed in terms of cetane number. The cetane number is obtained by comparing the behavior of the fuel in a test engine with the behavior of a mixture of cetane and alpha-methylnaphthalene. Diesel fuel oils of high cetane number are very desirable because of their quick detonation and smooth operation characteristics.

There is an increasing demand for diesel fuel oils having high cetane numbers and with progress in the design of diesel engines the requirement for diesel fuel oils gradually becomes more severe. To meet this augmenting demand, a present prevailing use is to blend straight run distillates with catalytically cracked fuels. However, since catalytically cracked oils tend to be lower in cetane number, the final blends also show a comparatively poor cetane rating. The use of diesel fuel oil low in cetane rating is very undesirable and is to be avoided since it detrimentally affects performance and reliability of compression-ignition engines.

Solvent extraction procedures have been used to a limited extent for improving the quality of diesel fuel oils but they are too expensive for wide-spread use. The ignition characteristics of diesel fuel oil may also be improved by suitable addition agents. These cetane-improving agents are usually added to the petroleum fuel oil base. Usage of cetane-improving additives permits the use of base fuels having relatively low cetane numbers to provide diesel fuel oil of desired characteristics and of good detonating qualities. At the present time, the available additives have not been sufliciently attractive for commercial acceptance, mainly because of price and effectiveness.

I have found that the addition to the petroleum fuel base of a small amount of the azo compounds defined below significantly improves the cetane rating of diesel fuels. By this invention, there is obtained fuel oil compositions for compression-ignition engines which perform more effectively than those heretofore obtained.

The organic azo compounds which I have found to be effective according to this invention may be represented by the following formula:

wherein the azo, N=N, group is tacyclic and bonded from both of the nitrogens to separate. carbons which are 2,877,102 Patented Mar. 10-, 1959 2 non-aromatic, i. e. aliphatic in nature. The said two aliphatic carbons are both tertiary carbons, i. e., they are joined to three other carbons by single valences. One of the carbons bonded to each of the said tertiary carbons has its remaining valences satisfied by at least one ele ment whose atomic number is seven to eight, i. e., by nitrogen and/or oxygen. The said carbon atom which is always singly bonded to the tertiary carbon has its re maining valences exclusively satisfied by nitrogen and/or oxygen and is part of a negative radical of the azo compounds. The negative radical generally is neutral with respect to acidity and there are two of such radicals for each azo compound, each negative radical being linked to one of the tertiary carbons. The said negative radical may differ from one azo compound to the other but these azo compounds are equally effective as cetane rating improvers, providing the carbon atom which is part of the negative radical is multiply linked only to oxygen and/or nitrogen, while the single remaining valence of said carbon is satisfied by the tertiary carbon atom linked to the azo nitrogen. Briefly, these azo compounds are all very effective as cetane rating improvers notwithstanding different negative radicals if as part of each negative radical there is a carbon atom linked to the tertiary carbon and only to nitrogen and oxygen,

For the purpose of this invention, the term saturated aliphatic hydrocarbon radical includes not only straight and branched open chains but also cyclic non-aromatic hydrocarbon chains. In the azo compounds which are effective cetane improvers, two of the valences of the tertiary carbon carried by the azo group may be satisfied by alkyl groups which are open-chained or by cycloalkyl groups. In another case, the respective tertiary carbons carried by the azo nitrogens are part of a saturated cycloalkyl hydrocarbon group which may be substituted by lower alkyl or not.

Some examples of compounds which, according to my invention, are effective cetane rating improvers are: 2,2-azobisisobutyronitrile; 2,2'-azobis-2,4-dimethylvaleronitrile; 2,2'-azobis-2-methylbutyronitrile; 2,2'-azobis-2- ethylbutyronitrile; 2,2'-azobis 2 methylheptanonitrile; 2,2'-azobis-2,3-dimethylbutyronitrile; 2,2-azobis-2,3,3-trimethylbutyronitrile; 2,2'-azobis-Z,4-dimethylcapronitrile; 2,2-azobis-2-n-butylcapronitrile; 2,2-azobis-2-isobutyl-4- methylvaleronitrile; 2,2 azobis-Z-ethyl-3-methylbutyronitrile; 2,2'-azobis-2,4,4-trimethylvaleronitrile; 2,2-azobis- 2-isopropylbutyronitrile; 2,2'-azobis 2 rnethyloctanonitrile; 2,2'-azobis-Z-methyl-n-nonadecanonitrile; 2,2-azobis-Z-methylhexadecanonitrile; 2,2-azobis-2-cyelopropylpropionitrile; 2,2'-azobis-2-cyclohexylpropionitrile; 2,2- azobis-2-cycloheptylbutyronitrile; 2,2'-azobis-2-cyclobutylpropionitrile; 2,2'-azobis 2 cyclopentylpropionitrile; 1,1-azodicyclopentane-l-carbonitrile; 1,1'-azodicyclobutane-l-carbonitrile; 1,1-azodicyclohexane-l-carbonitrile; 1,1-azodicycloheptane-l-carbonitrile; 1,1-azodi-3-methylcyclopentane-l-carbonitrile; l,1'-azodi-2-methylcyclohexane-l-carbonitrile; l,l'-azodi-2,4-dimethylcyclohexane-1- carbonitrile', 1,1-azodicyclooctane-l-carbonitrile; 1,1- azodicyclodecane-l-carbonitrile; and the corresponding primary, secondary, and tertiary amides and the esters of the above compounds in which the cyano group or groups are replaced by a negative radical characterized in that it contains a carbon atom multiply bound only to oxygen, and/ or nitrogen and to the tertiary carbon.

Because of their particular effectiveness, as'cetane. rating improvers and because of availability, the aliphatic azo nitriles and their corresponding esters are a particularly desirable class. 7

Among the effective azo compounds in addition. to those already mentioned are: 2,2'-azobisisobutyramide; 2,2 azobis 2,4-dimethylvaleramide; 2,2'-azobis-2-cyclopropylpropionamide; 1,1 ambis 2 dicyclohexane 1- o carbonamide; 1,1 azobis -'2 dicycloheptane l carbonamide; 1,1 azodicyclohexane 1 carboxylate; 2,2 azobis N,N' 1 diisobutyrodiethylamide; 2,2- azobis N,N' dimethylisobutyramide; 2,2-azobis-2,4-dimethyl 4 methoxyvaleronitrile; 2,2 azobis (lethylcarbonyl-cyclohexane) 2,2'-azobis- [Z-(rl-ethoxycarbonylethyl)propionitrile]; dimethyl alpha,alpha-azodiisobutyrate; diethyl alpha,alpha'-azodiisobutyrate; dihexyl alpha,alpha'-azodiisobutyrate. Preferably lower alkyl esters, e. g., of the 1-6 carbon alcohols are used as cetane rating improvers in view of their greater effectiveness in the fuel base on a weight basis and the ease and economy in preparing such esters.

The azonitriles may be prepared by the procedure described by Thiele and Hcuser, Ann. 290, l-43 (1896); Hartman, Recueil de Traveaux Chimiques 46, 150-153 (1927); Chem. weekblad, vol. 23, pages 77-78, January 1926; Box, I. Am. Chem. Soc. 4-7, 1471-1477 (1925 Alderson and Robertson in Patent No. 2,469,358, De Bonneville Patent No. 2,713,576, and Anderson in Patent No. 2,711,405.

A particularly effective and desirable method is that wherein the azine isolated from the reaction of the ketone and hydrazine is reacted with excess hydrogen cyanide containing less than 50% and preferably less than 10% Water to give the hydrazonitrile. The hydrazonitrile is readily oxidized by chlorine or bromine in aqueous medium to give the azonitrile. In such manner, for example, 2,2-azobis-2-methyl octanitriie may be prepared from hydrazine hydrate and methyl hexyl ketone.

The azonitrile can be converted to amides and esters, e. g., by formation of the iminoether hydrochloride by reaction with dry hydrogen chloride and an anhydrous alcohol followed by reaction with ammonia or the proper hydrogen-bearing amine, or with water. Thiele and Heuser, cited above, show the preparation of azo esters and amides. Likewise, the nltriles may be hydrolyzed to the carboxylic acid or the salt thereof in a conventional manner.

I have discovered that the addition of any of the cetane improvers of this invention produces a substantial improvement in the cetane number when added in a small concentration to a diesel fuel. Depending on the particular diesel fuel oil composition, the effect of any of these azo compounds is more or less marked; in all cases, the beneficial effect is significant. Addition of the azo compound in incremental amounts produces a corresponding improvement in cetane number over a definite range. The improvement depends on the composition of the base fuel and its cetane number and the particular azo compound used.

Generally, very satisfying improvement in the cetane rating is achieved when there is mixed with a diesel fuel oil an azo compound in an amount of about 0.1 percent to about 5 percent by weight, although in special cases more than 5% by weight may be used. Preferably, there should be added about 0.5% to about 1% by weight of the additive to a diesel fuel oil. The amount of additive recommended for optimum results depends on the additive selected and the type of fuel oil base with which it is used.

Those azo compounds which are of more limited solubility in the fuel oil may be added in amounts less than 1% by weight to the fuel oil and still be most effective in increasing the cetane number thereof.

The diesel fuels, to which according to this invention the azo compounds may be added, are the hydrocarbon fuels generally falling within a boiling range of 300 to 800 F. and may be composed of straight run or thermally or catalytically cracked components which may be treated or refined by conventional methods. The azo additives of this invention are of particular applicationto diesel fuel known as high speed diesel fuel. These fuels generally have a boiling range s of 350 to 650 F. Other characteristics of the fuels of this invention are: A. P. I. gravity of about 23 to 50, a diesel index of about to 80, a closed cup flash point of about 110 to 200 F., and a viscosity of about 350 thermoviscosity up to a Saybolt Viscosity of sec. at 100 F. It is apparent that this invention embraces fuel base stocks of general industrial use for compression ignition engines.

The azo compounds of this invention can be used in the presence of other additives. The fuel oil stocks to which the azo compounds are added may contain other additives or blending agents of all types such as stabilizers, color stabilizers, anti-corrosives, pour depressors, lubricants, dyes, gum inhibitors, oxidation inhibitors, carbon deposit reventives, and the like. In fact, the fuel oil base may also contain other types of cetane improvers or stabilizers of cetane improvers. in some cases, this may even be very advantageous since it appears that some synergistic effect may be obtained by the use of certain azo compounds eifective in this invention in conjunction with small amounts of other types of additives and fuel improvers. Similarly, according to this invention, mixtures of the azo compounds of this invention are sometimes very desirable and very effective in many cases to provide improved fuel oil compositions. Such an effective mixture may be prepared from any of the azo compounds described herein.

The azo compounds effective in this invention may be mixed with the fuel base at any time after refining or they may be added at storage time.

According to this invention, the azo compound cetanc I improvers may be added to the base fuel oil directly,

or alternatively they may be dissolved in a proper solvent and then added to the fuel in desired proportions.

The organic azo compounds eifective in this invention are stable and will not decompose under normal storage conditions. They have no apparent detrimental effect on the normal color upon addition and storage.

The following examples illustrate the beneficial effect and the utility of the azo compounds herein defined as improvers of the cetane rating of diesel fuel oils. A variety of fuel oils of different geographical sources, types and blends were tested. Tests were performed with samples of different catalytically cracked fuel oils, straight run stocks, and mixtures thereof. Some of the samples were of cetane number below minimum standard for satisfactory use; in all others the cetane number varied over a wide range. To the samples, there was added small amounts from about 0.2% to 2% by weight of selected azo compounds comprised in the general formula indicated above. In all cases, improvement in cetane rating was shown. In some cases, the improvement was more pronounced than in others, but in all cases the increase in cetane rating was significant. The increase varied from 5 to 20 octane numbers and in some cases exceeded 20.

in the examples below, the fuel used was Atlantic heating oil medium which is a diesel oil grade No. 2. This oil is defined in A. S. T. M., Standardson Petroleum Products and Lubricants, Philadelphia (1953), D975-53T, and it has the following specifications:

Gravity, A. P. I. at 60 (min.): 33-37; flash point, P. M. R: 130-160; viscosity at 100 F. kinematic centistolres: 214-427; pour point, F. (max): 0; color, A. S. T. M. Union calorimeter (max.): 3; water and sediment (main): trace; sulfur content, percent (max): 0.625; carbon residue, Conradson on 10% residuum, percent (max): 0.15; cetane number (min.): 45;distil1ation test, on volume recovered basis: 10%, F.- (max), 440, F. (max), 600; end point, F.-(max.):*640; free and corrosive sulfur, copper strip, 3 hours at 212 F: 1; burning index (min.): 65.

The method for determining the cetane numbers of the fuels was A. S. T. M. Test No. D613.

Typical results are summarized in Table I where-the azo compound shown is dimethyl alpha,alpha'-azodiisobutyrate which was dissolved into the fuel.

Diethyl alpha,alpha-azodiisobutyrate in a concentration range from 0.2 to 2% was then mixed with a sample of the above-described fuel oil. Upon testing the cetane number, improvement was essentially the same as shown in Table I.

When mixtures of diethyl alpha,alpha'-azodiisobutyrate and dimethyl alpha,alpha-azodiisobutyrate in different proportions are dissolved in the fuel oil base in concentrations from about 0.2 to 2%, the cetane rating is improved in all cases as much as shown in Table I; at concentrations at about 1.0%, even greater improvements in cetane ratings are obtained.

To further illustrate the usefulness as cetane improvers of the azo compounds described above, about 0.5% by weight of a selection of these compounds is dissolved in different fuel oil samples to which other additives and/ or blending agents have been added. The fuel oils are different grade fuel oils of the 1-D, 2-D (first and sectond section) and 4-D types as defined by the A. S. T. M. Tentative Classification (1952). The fuel oils represent petroleum distillates from different geographical districts compounded from straight runs or from catalytically cracked stock and mixtures thereof. The cetane rating varied widely. Cetane tests performed on the oil samples in the presence .of 0.5% by Weight dissolved azo compound in accordance with test D613 A. S. T. M. show that at definite concentrations the cetane rating increase is significant. Generally, the high cetane number increases are obtained by addition of the azo compound in oil samples with low initial cetane rating, but cetane increase is appreciable on all samples.

All tests on each fuel sample are performed at least in duplicate and the average cetane number is reported. Table II summarizes typical results. The azo compounds shown here are the liquid and solid isomers of 2,2'-azobis-2-methyloctanitrile when dissolved and tested in fuel oil described above.

The same test was performed in the presence of 1,1- azodicyclohexane- 1 -carbonitrile and of 2,2'-azobis-2- methylbutyronitrile in concentrations varying between 0.5 and 1.0%. Cetane number improvements were at least equivalent to those shown in Table II. 2,2-azobisisobutyronitrile showedthe same effect when dissolved and tested in the fuel oil. In all cases, there was obtained an improved compounded fuel oil ready for use in engines requiring high cetane fuels. Cetane ratings of the fuel oil were also shown to improve substantially when the fuel was tested in the presence of 2,2-azobisisobutyramide or with 2,2 -azobisisobutyronitrile.' The cetane ratings with these two compounds were substantially identical with those tabulated above. When 2,2- azobisisobutyronitrile and 2,2-azobis-2-methyloctanitrile are mixed in different ratios over a definite range of concentration and dissolved into the fuel oil, there is obtained cetane rating improvements substantially the same as those tabulated above.

0f the total sales of diesel fuel oil in the United States over the years 1950 to 1954 (in excess of 150,000,000 barrels in 1953 and 1954), a survey performed on representative samples of grade 1-D and first and second section 2-D shows that less than 5% gave a cetane test above 58; only about 1% showed a cetane test of 60. The majority of the diesel fuel tested gave a cetane number of about 52. Considerably higher cetane rating is much more desirable and such high and satisfactory levels can now be attained by following the teaching of this invention.

The organic compounds effective in this invention may be represented by the following formula:

Wherein -N=N is an acyclic azo group, said azo group having bonded to each nitrogen a discrete tertiary aliphatic carbon atom, wherein R and R taken individually represent saturated aliphatic hydrocarbons being alkyl or cycloalkyl radicals usually not over 19 carbon atoms each and preferably notover 9 carbon atoms each, or R and R where taken together form'an alkylene chain of 3 to 7 carbon atoms which jointly with the tertiary carbon carrying the nitrogen form a cycloalkyl group of 4 to 8 carbon atoms, said cycloalkyl groups being substituted with lower alkyl radicals or not, wherein X is a cyano radical, -CN, or a carbamoyl radical CONH or an N-substituted carbamoyl radical, an alkoxycarbonyl radical, COOR. Where X is an alkoxylcarbonyl, the alkyl group R thereof preferably is of 1 to 6 carbon atoms, and, in the respective -COOR radicals, the alkyl groups thereof are preferably, but not necessarily, alike. When X is an N-substituted carbamoyl radical, at least one hydrogen atom thereof is replaced by a lower alkyl radical to form the secondary and tertiary amides and the N-substituted radical may be shown as where n is an integer from 1 to 5. When X is a radical as defined above, there is contained'therein a carbon atom, one valence of which is satisfied by the tertiary carbon linked to the azo group and the remaining valences are satisfied by at least one element of an atomic number of seven to eight inclusive. Only two elements fit this qualification: nitrogen and oxygen.

While various specific embodiments of this invention have been described and illustrated, many modifications and adaptations may be made without departing from this invention, and all such changes are intended to be included in the claims.

I claim:

1. An improved diesel fuel oil for compression-ignition engines having dissolved therein a small quantity, at least sufficient to increase the cetane number of said oil, of-

organic azo compound having the formula 1 wherein N=N is an acyclic azo group, said azo group having bonded to each nitrogen a tertiary aliphatic carbon, wherein R and R when taken individually are saturated aliphatic hydrocarbon radicals of preferably not over 19 carbon atoms each, and R and R when taken together with the tertiary carbon carrying the azo nitrogen form a cycloalkyl group of 4 to 8 carbon atoms,

and wherein X is selected from the group consisting of (1) cyano, (2) carbamoyl, (3) alkoxycarbonyl, the alkyl groups thereof containing 1 to 6 carbons, and (4) the lower alkyl N-substituted carbamoyl.

2. All-improved diesel fuel oil for compression-ignition engines having dissolved therein a small quantity, at least suificient' to increase the cetane number of said oil from an initial cetane number of at least fifty, of an organic azo compound having the formula:

wherein N=N is an acyclic azo group, said azo group having bonded to each nitrogen a tertiary aliphatic carbon, wherein R and R when taken individually are saturated aliphatic hydrocarbon radicals of preferably not over 19 carbon atoms each, and R and R when taken together with the tertiary carbon carrying the azo nitrogen form a cycloalkyl group of 4 to 8 carbon atoms, and wherein. X is selected from the group consisting of (1) cyano, (2) carbamoyl, (3) alkoxycarbonyl, the alkyl groups thereof containing 1 to 6 carbons, and (4) the lower alkyl N-substituted carbamoyl.

3. An improved diesel fuel oil for compression-ignition engines having dissolved therein a small quantity from about 0.1% to about by weight of an organic azo nitrile having the formula wherein N=N 'is an acyclic azo group having bonded to each nitrogen a tertiary aliphatic carbon, wherein R and R when taken individually are saturated aliphatic hydrocarbon radicals of not over 19 carbon atoms each, and R and R when taken together with the tertiary carbon carrying the azo nitrogen form a cycloalkyl group of 4 to 8 carbon atoms, to increase the cetane number of said diesel fuel oil.

4. An improved diesel fuel oil for compression-ignition engines having dissolved therein a small quantity from about 0.1% to about 5% by weight of 2,2'-azobis-2-methylbutyronitrile to increase the cetane number of said diesel fuel oil.

5. An improved diesel fuel oil for compression-ignition engines having dissolved therein a small quantityfrom 8 about 0.1% about 5% by weight of v2,2 -a2:obis 2 m;=.thy1-, octanitrile.

6. An improved diesel fuel oil for'compression-ignition engines having dissolved therein from about 0.1% to about 5% by weight of 1,1'-azodicyclohexane-1-carbo nitrile to increase the cetane rating of said diesel fuel oil.

7. An improved diesel fuel oil for compression-ignition engines having dissolved therein asmall quantity from about 0.1% to about 5% by weight of an organic azo compound having the formula COOR wherein N=N is an acyclic'azo group having-bonded to each nitrogen a tertiaryaliphatic'carbon; wherein R and R when taken individually are saturated-aliphatic hydrocarbon radicals of not over 19 carbonatoms each, and R and R when taken together-with the tertiary carbon carrying the azo nitrogen form a cycloalkyl group of 4 to 8 carbon atoms, and where R is an alkyl from 1 to 6 carbons, to increase the cetane number of said diesel fuel oil.

8. An improved diesel fuel oil for compression-ignition engines having dissolved therein from about 0.l%*to about 5% by weight of dimethyl'alpha,alpha'-azodiisobutyrate.

9. An improved diesel fueloil for compression-ignition engines having dissolved therein a small quantity from about 0.1% to about 5% by weight of "an organic-azo compound having the formula wherein N=N is an acyclic azo group having bonded to each nitrogen a tertiary aliphatic carbon, wherein R and R when taken individually are saturated aliphatic hydrocarbon radicals of not over 19 carbonatoms each, and R and R when taken together-with the tertiary carbon carrying the azo nitrogen form a cycloalkyl group of 4 to 8 carbon atoms, and where n is an integer from 1 to 5, to increase the cetane number of said diesel fuel oil.

10. An improved diesel fuel oil for compressionfignition engines having dissolved therein from about 0.1%5 to about 5% by weight of 2,2' azobisisobutyramide.

References Cited in the file'of this'patent UNITED STATES PATENTS 2,225,879 Miller et a1. Dec. 24, 1940 2,392,611 Nygaard et al. Ian. 8, 1946 2,655,440 Barusch et al. Oct. 13, 1953 2,713,576 De Benneville July19, 1955 OTHER REFERENCES Petroleum Refining With Chemicals, 'Kalichevsky and Kobe, Elsevier Pub. Co., 1956, pp. 510 and 511.. 

1. AN IMPROVED DIESEL FUEL OIL FOR COMPRESSION-IGNITION ENGINES HAVING DISSOLVED THEREIN A SMALL QUANTITY, AT LEAST SUFFICIENT TO INCREASE THE CETANE NUMBER OF SAID OIL, OF AN ORGANIC AZO COMPOUND HAVING FORMULA 